The present invention relates to fuel injectors of the type used in an internal combustion engine.
Japanese Application Patent Laid-Open Publication No. Hei 08-42427 discloses a fuel injector for an internal combustion engine, in which a valve member slidable in its axial direction is provided inside a body having a cross-sectionally round injection hole as an open end. A swirling force generating means for imparting a swirling component to fuel is disposed between the outer surface of the valve member and the inner surface of the body. The base end portion of the injection hole is open on the axial center line of the injector, but the open edge of the front open end of the injection hole is not disposed along a plane orthogonal to the center line of the injection hole. More specifically, the open edge of the front open end of the injection hole in the fuel injector is disposed along a plane that is inclined with respect to the center line of the injection hole. In this fuel injector, the center line of the fuel spray spreading in approximately a conical form, namely, the direction of the spray, is inclined with respect to the center line of the injection hole, and does not extend along the center line.
Japanese Application Patent Laid-Open Publication No. Hei 10-184496 discloses a fuel injector wherein a fuel injection chamber that is opened and closed by a needle valve is formed at the front end of a valve body containing a needle valve. An injection hole is formed obliquely at the bottom of the fuel injection chamber, and the fuel pumped into the valve body, when the needle valve opens, is supplied spirally to the inside of the fuel injection chamber and is injected from the injection hole. The fuel injector has a unidirectional-offset suppression means by which the unidirectional offset of the velocity distribution of the fuel flowing into the injection hole, in the axial direction of the injection hole, is suppressed.
More specifically, the slope of the inclined surface from the fuel injection chamber to the injection hole is set so as to change according to the particular circumferential position of the injection hole. Even more specifically, the inner lower surface of the fuel injection chamber is formed into a semi-spherical shape, and the position of the injection hole is offset in a direction such that it is rotated through 90 degrees with respect to the swirling direction of the fuel from the direction of inclination of the injection hole. In this fuel injector, the spray status of the fuel injected from the outlet of the injection hole is homogenized by the unification of the axial velocity distribution of the fuel inside the injection hole.
The above-described technology presents a method of changing the shape of the spray produced by a fuel injector. For an in-cylinder direct injection-type gasoline engine (hereinafter, referred to as a direct injection engine), in particular, the spray of fuel that has been formed into an appropriate shape, depending on the combustion scheme, the shape of the combustion chamber, the dimensions thereof, and other factors, and the value of the corresponding fuel injector is great.
However, for the fuel injector disclosed in Japanese Application Patent Laid-Open Publication No. Hei 0842427, since the angle of inclination of the fuel injection direction has a correlation with the spray angle of the injected fuel, the degree of freedom in the formation of the injection direction and spray angle of the fuel is never high. For example, there is a problem in that the inclination of the fuel injection direction also causes an offset in the concentration distribution of the fuel, and the desired spray is not easy to obtain.
For the fuel injector disclosed in Japanese Application Patent Laid-Open Publication No. Hei 10-184496, the injection hole has a function that determines the injection direction of the fuel, in addition to a function that measures the injection volume. Therefore, there is a problem in that the decentering of the injection hole changes the volume of the fuel injection. That is to say, since the injection hole is provided in eccentric form in the semi-spherical fuel injection chamber, the area and shape of the section ranging from the fuel injection chamber to the injection hole will change according to the amount of eccentricity thereof, and these factors affect the flow rate of the fuel. Conversely, if the diameter of the injection hole is changed to compensate for a change in injection volume, the amount of eccentricity of the injection hole will also change, which will make it difficult to obtain both the desired injection volume and spray shape.
In addition, it is not easy to provide an inclined injection hole in a curved fuel injection chamber by simply piercing, in eccentric form, the member constituting the injection hole, or to provide a member that has an inclined and eccentric injection hole, with curved-surface machining appropriate for the fuel injection chamber; and so, the use of these machining processes causes an increase in cost when the fuel injector is to be manufactured by mass production.